Concurrent Psoriasis and Dermatomyositis: Retrospective Analysis and Literature Review

ABSTRACT Background Psoriasis (PsO) and dermatomyositis (DM) are both autoimmune‐mediated, inflammatory conditions. The concurrence of PsO and DM is rare, and literature on their relationship remains limited. Additionally, cutaneous DM can be challenging to clinically diagnosis, often presenting with psoriasiform clinical features. Objectives Our primary objective was to characterise concurrent PsO and DM, describing demographic, clinical, and temporal patterns among verified cases from institutional medical records and medical literature. A secondary objective was to determine the patients initially thought to have PsO but instead had psoriasiform changes related to DM (misdiagnoses). Methods A retrospective chart review was conducted on patients with ICD‐10 codes for PsO and DM. Diagnoses were confirmed through evaluation of clinical features, histopathology, and serologic testing. Literature review was performed with the terms “psoriasis” and “dermatomyositis.” Categorical variables were analysed with Fisher's exact test, and continuous variables with two‐sample t ‐tests. Results We identified four patients with concomitant PsO and DM at our institution and 20 cases in the medical literature, for a total of 24 patients. Of those with documented history, 50% (3/4) had other autoimmune conditions, and 75% (6/12) had a family history of autoimmunity. DM preceded PsO in 54% (13/24) of cases with an average of 7.1 years between diagnoses. PsO often presented during steroid withdrawal (7/13, 54%). Of the cases in which PsO preceded DM, 7.4 years occurred between diagnoses. A significant portion received PsO biologics (5/11, 45%) or phototherapy (2/11, 18%) before DM onset. Patients with DM before PsO had more extensive psoriatic skin disease involving the trunk and extremities compared to those who later developed DM ( p < 0.0001). Of note, at our institution, we identified 10/14 (71%) verified cases of DM in which patients initially had been misdiagnosed with PsO based on skin examination. Conclusions We present the first case series and largest analysis of concomitant PsO and DM. The high rate of DM being misdiagnosed with PsO highlights the difficulty of distinguishing between true overlap versus psoriasiform‐like rashes known to be associated with DM. Concurrent disease should be more suspected in those with personal or family history of autoimmunity, when rashes of differing behaviour or morphology appear years apart, and when therapy for one might have induced the other.